linux-kernel - Re: [PATCH v19 02/13] x86/setup: Use parse_crashkernel_high

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <933554c7-1fc6-8e7a-9569-9f8441e50ddf@huawei.com>
Date:   Thu, 30 Dec 2021 10:39:12 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Borislav Petkov <bp@...en8.de>
CC:     Dave Young <dyoung@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>, <x86@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>, <linux-kernel@...r.kernel.org>,
        Baoquan He <bhe@...hat.com>, Vivek Goyal <vgoyal@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        <kexec@...ts.infradead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        "Will Deacon" <will@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        <devicetree@...r.kernel.org>, Jonathan Corbet <corbet@....net>,
        <linux-doc@...r.kernel.org>, Randy Dunlap <rdunlap@...radead.org>,
        Feng Zhou <zhoufeng.zf@...edance.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        "Chen Zhou" <dingguo.cz@...group.com>,
        John Donnelly <John.p.donnelly@...cle.com>
Subject: Re: [PATCH v19 02/13] x86/setup: Use parse_crashkernel_high_low() to
 simplify code

On 2021/12/30 0:51, Borislav Petkov wrote:
> On Wed, Dec 29, 2021 at 11:04:21PM +0800, Leizhen (ThunderTown) wrote:
>> Chen Zhou and I tried to share the code because of a suggestion. After so many
>> attempts, it doesn't seem to fit to make generic. Or maybe I haven't figured
>> out a good solution yet.
> 
> Well, you learned a very important lesson and the many attempts are not
> in vain: code sharing does not make sense in every case.
> 
>> I will put the patches that make arm64 support crashkernel...high,low to
>> the front, then the parse_crashkernel() unification patches. Even if the
>> second half of the patches is not ready for v5.18, the first half of the
>> patches is ready.
> 
> I think you should concentrate on the arm64 side which is, AFAICT, what
> you're trying to achieve.

Right, a patchset should focus on just one thing.

> 
> The "parse_crashkernel() unification" needs more thought because, as I
> said already, that doesn't make a whole lot of sense to me.

Yes, because it's not a functional improvement, it's not a performance optimization,
it's also not a fix for a known bug, it's just a programmer's artistic pursuit.

> 
> If you want to enforce the fact that "low" makes sense only when "high"
> is supplied, parse_crashkernel_high_low() is not the right thing to do.
> You need to have a *single* function which does all the parsing where
> you can decide what to do: "if high, parse low", "if no high supplied,
> ignore low" and so on.

I understand your proposal, but parse_crashkernel_high_low() is a cost-effective
and profitable change, it makes the current code a little clearer, and avoid passing
unnecessary parameters "system_ram" and "crash_base" when other architectures use
parse_crashkernel_{high|low}().

I actually followed your advice in the beginning to do "parse_crashkernel() and
parse_crashkernel_{high|low}() unification". But I found it's difficult and the
end result may not be as good as expected. So I introduced parse_crashkernel_high_low().

The parameter "system_ram" and "crash_base" of parse_crashkernel() is not need by
"crashkernel=X,[high,low]". And parameter "low_size" of parse_crashkernel_high_low()
is not need by "crashkernel=X[@offset]". The "parse_crashkernel() unification"
complicates things. For example, the parameter "crash_size" means "low or high" memory
size for "crashkernel=X[@offset]", but only means "high" memory size for "crashkernel=X,high".
So we'd better give it two names with union.

> 
> And if those are supported on certain architectures only, you can do
> ifdeffery...

I don't think so. These __init functions are small and architecture-independent, and do not
affect compilation of other architectures. There may be other architectures that use
it in the future, such as the current arm64.

> 
> But I think I already stated that I don't like such unifications which
> introduce unnecessary dependencies between architectures. Therefore, I
> won't accept them into x86 unless there's a strong compelling reason.
> Which I don't see ATM.

OK.

> 
> Thx.
> 

-- 
Regards,
  Zhen Lei